I tested making flex sensors with paper, copper tape, and velostat.  I tested how the number of rows of copper tape effected the sensitivity of the sensor.

Hypothesis:  (1) Increasing the number of rows of copper tape on one side of the paper will make the flex sensor more sensitive.  (2) If you wrap the rows around to both sides of the paper, it will decrease the sensitivity.

Results:

Tape on both needs of the paper made the sensor more sensitivity; therefore, the user does not need to bend or squeeze the sensor very much to see the full brightness of the LED.

Tape on one side of the paper created the best sensor in terms of not being too sensitive and not sensitive enough.

One row of tape was the least sensitive sensor, and the user needed to bend the sensor a lot.  Even if the sensor was bent in half, the sensor did not .  However, you could squeeze the sensor very tightly to see the full brightness of the LED.